Electric supercharging device and multi-stage supercharging system

ABSTRACT

It is intended to provide: an electric supercharging apparatus wherein, with a simple structure, rotor windage loss in an electric motor for driving a compressor is reduced and good cooling performance is produced; and a multi-stage supercharging system using the electric supercharging device. This electric supercharging apparatus is provided with: a first cooling passage formed in a stator along a motor coil and communicating a gas supply port with a gas discharge port in a motor housing; and a first intake passage connecting the gas discharge port to an intake port of a compressor. This electric supercharging apparatus is configured to introduce outside air into the first cooling passage via the gas supply port by applying negative pressure to the first cooling passage via the first intake passage, thereby cooling the inside of the motor housing.

This application is a Continuation of application Ser. No. 14/122,141,filed on Dec. 16, 2013, which was filed as PCT International ApplicationNo. PCT/JP2012/067149 on Jul. 5, 2012, which claims priority under 35USC §119(a) of Japanese Application No. 2011-156521, filed in Japan onJul. 15, 2011, all of which are hereby expressly incorporated byreference into the present application.

TECHNICAL FIELD

The present invention relates to the technical field of an electricsupercharging device for supercharge of an internal combustion enginesuch as an engine by being driven by an electric motor for, and of amulti-stage supercharging using the electric supercharging device.

BACKGROUND ART

In an internal combustion engine such as an engine, there is a casewhere the intake air is compressed and supplied using a superchargingapparatus such as a turbocharger, thereby increasing output. As one typeof this supercharging apparatus, there is a turbocharger which isconfigured to rotate a turbine at high speed using energy of the exhaustgas and drive a centrifugal compressor by the rotational force so as tofeed the compressed air into the engine. However, the superchargingpressure is decreased when the engine speed is low in the turbocharger.And sufficient increase of the output cannot be expected. On the otherhand, the electric supercharging apparatus which his drive by anelectric motor has the advantage that a predetermined superchargingpressure can be obtained even at low engine rotation speed.

Since a rotor of the electric motor is generally provided withconvex-shaped pole on its surface, as the motor rotation speedincreases, a substantial amount of windage loss occurs due to theirregular surface shape. This can cause not only the power loss of theelectric motor but wind noise caused by the rotor, which can lead to thenoise increase. In order to reduce this power loss and noise, designchange of the rotor may be considered, but there is a limit to this inreality. To solve this issue, it is taught, for instance in PatentDocument 1, to seal the periphery of the rotor of the electric motor ina reduced pressure state so as to reduce air resistance of the rotor andalso achieve improved power efficiency and reduced noise.

When the motor speed rises, calorific value increases in the motor coilwhere the current flows, an inverter part for the motor control, or thelike. Especially when the electric motor is accelerated or when a largeload is applied, a large current flows and the calorific valueincreases. Thus, a cooling mechanism is required. There are many typesof cooling mechanisms such as air-cooled or water-cooled coolingmechanism. For instance, disclosed in Patent Document 2 is anair-cooling mechanism in which, by utilizing the differential pressurebetween the atmospheric pressure and the compressor outlet pressurepressurized by the electric motor, a portion of the compressed air issprayed to the vicinity of the rotor.

CITATION LIST Patent Document

[Patent Document 1] JP 9-19100 A

[Patent Document 2] JP 2006-257994 A

SUMMARY Technical Problem

As described above, reduction in windage loss of the rotor and improvedcooling performance of the internal heat generation are desired in theelectric motor. However, there is a problem when trying to provide thedecompression means or the cooling mechanism as described in PatentDocument 1 and Patent Document 2 in order to satisfy these requirements.Specifically, the configuration of the electric motor is undesirablycomplicated. Further, the compressed air used for cooling in PatentDocument 2 is high-pressure and high-temperature, there is a problemthat the cooling efficiency is low and a sufficient cooling performancecannot be expected.

The present invention has been made in view of the above problems, andan object of the present invention is to provide an electricsupercharging apparatus and a multi-stage supercharging system using theelectric supercharging apparatus, which can achieve reduction of thewindage loss of the rotor and improved cooling performance in theelectric motor which drives the compressor.

Solution to Problem

To solve the above issues, an electric supercharging apparatus accordingto the present invention is configured to rotate an electric motor thatcomprises a rotor shaft rotatably supported in a motor housing to whicha motor coil and a stator are fixed, so as to drive and supercharge acompressor connected to one end of the rotor shaft, and the electricsupercharging apparatus according to the present invention comprises: agas supply port and a gas discharge port which are provided in the motorhousing; a first cooling passage which communicates the gas supply portand the gas discharge port in the motor housing and which is formed inthe stator along the motor coil; and a first intake passage whichconnects the gas discharge port to an inlet port of the compressor.Further, outside air is introduced to the first cooling passage from thegas supply port using a negative pressure of the inlet port of thecompressor applied to the first cooling passage via the first intakepassage.

According to the present invention, the outside air is introduced to thefirst cooling passage from the gas supply port by applying the negativepressure of the inlet port of the compressor to the first coolingpassage via the first intake passage, so as to cool the vicinity of thefirst cooling passage where heating is likely to occur (such as a statorand a motor coil). According to the present invention, as describedabove, the outside air is introduced using the negative pressure of thecompressor without an energy-consuming configuration such as a pump.Therefore, it is possible to effectively cool the interior of the motorhousing which generates a large amount of heat, with a simpleconfiguration. In particular, the air introduced into the first coolingpassage is not supercharged air of high temperature but is the outsideair. Thus, it is possible to obtain an excellent cooling effect.

Preferably, a second cooling passage is also provide, which connects thegas supply port to the gas discharge port in the motor housing and whichis formed along the rotor shaft between the rotor shaft and itsperipheral member, and the second cooling passage joins the firstcooling passage in the motor housing so that the outside air isintroduced to the second cooling passage from the gas supply port by anegative pressure applied via the first intake passage. Generally, thereis at least a small gap formed around the rotor shaft to prevent contact(or collision) with the peripheral member when the rotor shaft isrotated. The second cooling passage is configured to also serve as thegap, and by applying a negative pressure thereto, the outside air isintroduced from the gas supply port to cool the vicinity of the rotorshaft to which the heat is easily transferred from the motor coil andthe stator with high heat value. Further, the second cooling passage isreduced in pressure by the negative pressure applied thereto and thus,it is possible to reduce air resistance of the rotor shaft and thewindage simultaneously. Furthermore, the first cooling passage and thesecond cooling passages are configured to join together in the motorhousing and thus, the outside air can be introduced to the secondcooling passage by a negative pressure applied via a single first intakepassage. This is advantageous in that a significant cooling effect canbe obtained with a simple structure.

The above electric supercharging apparatus may further comprise aninverter unit which comprises an element circuit board housed in aninverter housing, the inverter unit being mounted on a side of the motorhousing where the gas supply port is formed, and an air hole to let theoutside air through to the gas supply port may be provided on theelement circuit board. Generally, the inverter unit for control of theelectric motor is another component that generates heat easily. In thisaspect of the present invention, by providing an air hole on the elementcircuit board belonging to the inverter unit, it is possible to let theoutside air through to the gas supply port of the motor housing so as tocool. Further, by installing the inverter unit in the motor housing, thedistance between the electric motor and the inverter can be shorter andthe electric power loss therebetween can be minimized.

The above electric supercharging apparatus may further comprise: a firstcontrol valve for adjusting an opening of the first intake passage; anda controller for controlling an opening degree of the first controlvalve. According to this aspect, by adjusting the opening degree of thefirst control valve, it is possible to change the value of the negativepressure applied to the first cooling passage and to control the amountof the outside air being introduced. As a result, it is possible toadequately regulate the cooling level.

In this case, the electric supercharging apparatus may further comprise:a negative-pressure supply part which is connected to the gas supplyport via the second intake passage to apply a negative pressure to thefirst cooling passage; and a second control valve for adjusting anopening of the second intake passage, and the controller may beconfigured to control the opening degree of the first control valve andan opening degree of the second control valve. According to this aspectof the present invention, if sufficient negative pressure for coolingcannot be obtained via the first intake passage, the opening degree ofthe second control valve is adjusted to supplementarily supply thenegative pressure from the negative-pressure supply part. As a result,the cooling performance can be improved.

Moreover, a plurality of the first cooling passages may be provided tosurround the motor coil in a section orthogonal to the rotor shaft. Themotor coil is a component having a large heat value. Thus, in thisaspect, the first cooling passages are provided surrounding the motorcoil so as to suppress the temperature rise of the motor coil and alsoto obtain an excellent cooling performance.

Further, the first cooling passage may be configured in part to includean outer wall surface of the motor coil. According to this aspect, theoutside air flowing in the first cooling passage contacts the wallsurface of the motor coil directly, thereby drawing heat from the motorcoil. As a result, it is possible to achieve an excellent coolingperformance.

To solve the above issues, a multi-stage supercharging system accordingto the present invention comprises: the electric supercharging apparatusas described above; and a pre-stage supercharger which is arranged on anupstream side with respect to the electric supercharging apparatus andwhich is configured to supercharge gas in a pre-stage and supply to theelectric supercharging apparatus. In this multi-stage superchargingsystem, the compressed gas having been supercharged by a pre-stagesupercharger, such as a turbocharger, arranged on the upstream side (thelow pressure side) is supplied to the above electric superchargingapparatus so as to perform supercharging in multiple stages and increasethe supercharging pressure. As a result, the high supercharging pressurecan be obtained and thus, it is possible to realize the system capableof performing even when the required output is large, such as duringacceleration.

Preferably, the first intake passage is connected to an inlet port whichis provided on an intake side of the pre-stage supercharger. Accordingto this aspect, by connecting the first intake passage to the inlet portof the pre-stage supercharger which has high negative pressure at theinlet port compared to the electric supercharging apparatus disposed onthe downstream side, it is possible to apply a large negative pressureto the above cooling passage formed in the motor housing, therebyachieving a good cooling performance. Further, a significant pressurereduction effect in the cooling passage can be obtained. As a result,air resistance around the rotor shaft is reduced, thereby contributingto reduction of the windage loss.

Advantageous Effects

According to the present invention, the outside air is introduced to thefirst cooling passage from the gas supply port by applying the negativepressure of the inlet port of the compressor to the first coolingpassage via the first intake passage, so as to cool the vicinity of thefirst cooling passage where heating is likely to occur (such as a statorand a motor coil). According to the present invention, as describedabove, the outside air is introduced using the negative pressure of thecompressor without an energy-consuming configuration such as a pump.Therefore, it is possible to effectively cool the interior of the motorhousing which generates a large amount of heat, with a simpleconfiguration. In particular, the air introduced into the first coolingpassage is not supercharged air of high temperature but is the outsideair. Thus, it is possible to obtain an excellent cooling effect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an overall configuration of anelectric supercharging apparatus according to a first embodiment.

FIG. 2A illustrates one configuration of a first cooling passage in anelectric motor.

FIG. 2B illustrates another configuration of the first cooling passagein the electric motor.

FIG. 2C illustrates yet another configuration of the first coolingpassage in the electric motor.

FIG. 3 is a cross-sectional view of the overall configuration of theelectric supercharging apparatus according to a second embodiment.

FIG. 4 is a block diagram of an overall configuration of an electric2-stage supercharging system according to a third embodiment.

DETAILED DESCRIPTION

The present invention will now be described in detail using embodimentsshown in the accompanying drawings. It is intended, however, that unlessparticularly specified in these embodiments, dimensions, materials, andshapes of components, their relative positions and the like shall beinterpreted as illustrative only and not limitative of the scope of thepresent invention.

First Embodiment

FIG. 1 is a cross-sectional view of an overall configuration of anelectric supercharging apparatus 1 according to a first embodiment. Theelectric supercharging apparatus 1 is provided with a compressor 2 forsupercharging gas, an electric motor 3 for driving the compressor 2 andan inverter unit 4 functioning as an inverter for control of theelectric motor 3. The inverter unit 4 obtains DC current power from abattery (not shown) and changes the current and voltage applied to theelectric motor 3 so as to control the rotation speed of the electricmotor 3.

The inverter unit 4 and the electric motor 3 are integrally connected soas to reduce the distance between the inverter unit 4 and the electricmotor 3, thereby minimizing electrical loss of the power supplied to theelectric motor 3. In the case where the electrical loss is not an issue,the electric motor 3 and the inverter unit 4 may be arranged away fromeach other as separate units.

In the compressor 2, the gas drawn from the inlet port 5 is pressurizedby a compressor wheel 6 which is rotated by the electric motor 3 andthen discharged from a discharge port (not shown) through an interior ofthe compressor cover 7, so as to supercharge to an intake system of theinternal combustion engine such as an engine. The compressor wheel 6 isaccommodated in an inner central portion of the compressor cover 7. Thecompressor wheel 6 is connected to one end of a rotor shaft of theelectric motor 3 to be rotationally driven.

The electric motor 3 is provided with a stator 9 (a stator) which isfixed to the interior of the motor housing 8 and a rotor shaft 10 (arotator) which is rotatable around the rotor shaft 10. Inside the motorhousing 8, the rotor shaft 10 is supported by rolling bearings 12 a and12 b from both sides thereof to be rotatable around the rotation shaft.

Particularly in this embodiment, used as the rolling bearings 12 a and12 b are grease enclosed rolling bearings with seal which are providedwith grease leakage prevention measures at high rotation speed. By usingthe grease enclosed rolling bearings with seals as described above, itis no longer necessary to supply lubricating oil from outside of theelectric supercharging apparatus 1 (e.g. from the engine) as in the caseof using rolling bearings of oil-lubricated type. Thus, it is possibleto omit an introduction path for lubricating oil and also simply theinternal structure of the electric motor 3.

In this embodiment, described is a two-end support type where both endsof the rotor shaft 10 of the electric motor 3 are respectively supportedby the rolling bearings 12 a and 12 b. This is, however, not limitativeand the present invention is also applicable to a one-end support typewhere only one end of the rotor shaft 10 is supported by a rollingbearing.

If the lubricating oil is used in the rolling bearing 12, thelubricating oil is supplied from the engine or the like and thus, it isnecessary to arrange the electric supercharging apparatus 1 at aposition near the engine, where it is subjected to high temperature andfrequent vibration. However, by using the grease enclosed rollingbearing described in this embodiment, supply of the lubricating oil isno longer necessary and thus, the installation location of the electricsupercharging apparatus 1 is not subject to the above limitation.Therefore, the electric supercharging apparatus 1 can be mounted to avehicle body or the like with little vibration and good ventilationwhich is far from the engine and suitable for cooling. This improves thedegree of freedom of installation layout.

Further, the electric power energy supplied from the inverter unit 4 ismainly used to drive the electric motor 3 and is at least in partconverted into heat energy as heating. In particular, heat generation islikely to occur in a motor coil 11 under high loads and acceleration ofthe electric motor 3 and thus, cooling thereof is important. In thepresent embodiment, cooling passages are formed in the motor housing 8,and cooling is performed by the outside air introduced to the coolingpassages as described below.

In the motor housing 8, a gas supply port 13 and a gas outlet 14 areformed to introduce and discharge the outside air into and from thecooling passage. The gas supply port 13 is provided on the side of themotor housing 8 facing the inverter unit 4, and a plurality of thesupply ports is formed corresponding to the inlets of the first coolingpassage and the second cooling passage which are described later (inFIG. 1, the gas supply port corresponding to the inlet of the firstcooling passage is “13 a” and the gas supply port corresponding to theinlet of the second cooling passage is “13 b”). The gas discharge port14 is provided on the side surface of the motor housing 8, which is onthe compressor 2 side.

An intake passage 15 is an example of the “first intake passage”according to the present invention. The intake passage 15 is provided soas to connect the gas discharge port 14 and the negative-pressure outletport 16 which is formed by opening a hole on the side of the compressorcover 7. The intake passage 15 is, for example, made of a tubular membersuch as a rubber hose, but the material is not particularly limited. Onthe side wall of the compressor cover 7, the negative-pressure outletport 16 is formed so as to communicate with the interior of thecompressor cover 7, and the negative pressure generated inside thecompressor cover 7 is drawn out from one end of the intake passage 15 byrotation of the compressor wheel 6. The other end of the intake passage15 is connected to the gas discharge port 14 provided in the motorhousing 8 and is configured so that the negative pressure is applied tothe cooling passage formed inside the motor housing 8 from the gasdischarge port 14.

The gas supply port 13 communicates with the gas discharge port 14inside the motor housing 8 via the first cooling passage 17, and thefirst cooling passage 17 is formed along the motor coil 11 in the stator9. This first cooling passage 17 communicates with the intake passage 15via the gas discharge port 14. As the negative pressure transmitted fromthe negative-pressure outlet port 16 is applied to the first coolingpassage 17, the outside air is drawn into the first cooling passage 17from the gas supply port 13. The outside air introduced into the firstcooling passage 17 flows through the motor housing 8 as indicated byarrows in FIG. 1 and then introduced to the inlet port 5 of thecompressor 5 from the negative pressure outlet port 16 via the intakepassage 15.

The first cooling passage 17 is formed as described above to extendalong the motor coil 11 which generates a large amount of heat, and thusby allowing the flow of the outside air therein, good coolingperformance can be obtained. In particular, the outside air isintroduced by the negative pressure of the compressor 2 without anenergy-consuming structure such as a pump and thus, it is possible toeffectively cool the interior of the motor housing 8 which generates alarge amount of heat, with a simple configuration in the presentinvention. The air introduced into the first cooling passage 17 is notsupercharged air of high temperature but is the outside air. Thus, it ispossible to obtain an excellent cooling effect.

Referring to FIG. 2A, FIG. 2B and FIG. 2C, configuration examples of thefirst cooling passages 17 in the electric motor 3 are described. FIG.2A, FIG. 2B and FIG. 2C are cross-sectional views illustratingconfiguration examples of the first cooling passage 17 inside theelectric motor 3. The most simple example is illustrated in FIG. 2Awhere the first cooling chamber 17 is provided for each of the motorcoils 11. Particularly, in FIG. 2A, the first cooling passage 17 isprovided between the stators 9 so that an outer wall surface of themotor coil 11 constitutes a part of the cooling passage 17. As a result,the surface of the motor coil 11 is directly cooled by the outside airflowing in the first cooling passage 17. Thus, it is possible to obtainan excellent cooling effect.

Further, as illustrated in FIG. 2B and FIG. 2C, a plurality of the firstcooling passages 17 may be provided for each of the motor coils 11. Byproviding more first cooling passages 17 in this fashion, it enhancesthe cooling performance and it is possible to deal with a larger heatgeneration. Furthermore, in the case of providing a plurality of thefirst cooling passages 17 in this fashion, the first cooling passages 17may be arranged to surround the motor coil 11 in a section orthogonal tothe rotor shaft 10. Particularly, by arranging the first coolingpassages 17 so that a portion of each of the first cooling passages 17includes the outer wall of the motor coil 11 as illustrated in FIG. 2C,the outside air directly contacts a larger area of the surface of themotor coil 11, thereby achieving improved cooling effect.

The shape, number and area of the first cooling passage 17 illustratedin FIG. 1, FIG. 2A, FIG. 2B and FIG. 2C may be appropriately changeddepending on heat value (thermal load) of the motor coil 11 which is aheat generating source. As specific examples of the cross-sectionalshape of the first cooling passages 17, crescent, circular andelliptical shape may be considered.

Returning to FIG. 1, similarly to the first cooling passage 17, a secondcooling passage 18 is formed in the motor housing 8 so as to communicatewith the gas supply port 13 and the gas exhaust port 14. In particular,in communication with the gas exhaust port 14 and the gas supply port 13in the motor housing 8, the second cooling passage 18 is formed alongthe rotor shaft 10 between the rotor shaft 10 and a peripheral member ofthe rotor shaft 10.

Generally, there is at least a small gap formed around the rotor shaft10 to prevent contact (or collision) with the peripheral member when therotor shaft 10 is rotated. The second cooling passage 18 is configuredto also serve as the gap, and by applying a negative pressure to thesecond cooling passage 18, the outside air is introduced from the gassupply port 13 into the second cooling passage 18, thereby cooling thevicinity of the rotor shaft 10 to which the heat is easily transferredfrom the motor coil 11 and the stator 9 with high heat value. Further,the second cooling passage 18 is reduced in pressure by the negativepressure applied thereto and thus, it is possible to reduce airresistance of the rotor shaft 10, thereby also reducing the windage losssimultaneously.

The second cooling passage 18 joins the first cooling passage 17 insidethe motor housing 8, and the negative pressure is applied to the secondcooling passage 18 as well as the first cooling passage 17 from theintake passage 15, thereby introducing the outside air from the gassupply port 13. By configuring the first cooling passage 17 and thesecond cooling passage 18 so as to join together in the motor housing 8,it is possible to introduce the outside air into these two coolingpassages 17 and 18 by applying the negative pressure by means of asingle intake passage 15. As a result, it is possible to obtain a largecooling effect with a simple structure.

Further, the second cooling passage 18 is formed so as to run throughthe periphery of the rolling bearing 12 supporting the rotor shaft 10.Furthermore, the second cooling passage 18 is configured to cool therolling bearing 12 in addition to the rotor shaft 10. The interior ofthe electric motor 3 is basically made of a metal material having goodthermal conductivity and thus, the heat is easily transferred to therolling bearing 12 from the motor coil 11 side and the temperature riseseasily. In the present embodiment, by providing the second coolingpassage 18 passing through the rolling bearing 12 as well as the rotorshaft 10, it is possible to realize efficient cooling of these partswith simple configuration.

In the intake passage 15, a control valve 19 for adjusting the openingof the intake passage 15 is provided. The control valve 19 is an exampleof a “first control valve” according to the present invention, and byadjusting the opening degree of the control valve 19, the flow rate ofthe gas through the intake passage 15 is regulate, and the value of thenegative pressure transmitted to the first cooling passage 17 and thesecond cooling passage 18 is controlled. As a result, the flow rates ofthe gas in the first cooling passage 17 and the second cooling passage18 are adjusted to perform the cooling according to the heat value ofthe motor coil 11.

The opening degree of the control valve 19 is adjusted based on acontrol signal from a controller 20. The controller 20 is an example ofthe “controller” according to the present invention. For instance, thetemperature of the motor coil 11 which is a cooling object is detectedby a temperature sensor (not shown) attached to the motor coil 11 andthe control signal is transmitted to the control valve 19 based on thedetection value so as to adjust the opening degree of the control valve19. In the present invention, cooling is performed by drawing in theoutside air by applying the negative pressure to the first coolingpassage 17 and the second cooling passage 18, and as the negativepressure is applied from the inlet port 5 of the compressor 2, thesupercharging efficiency of the compressor 2 decreases to some extent.However, by adjusting the opening degree of the control 19 appropriatelyin accordance with the temperature of the motor coil 11 in the abovemanner, it is possible to avoid application of the negative pressuremore than necessary. Therefore, it is possible to prevent decline of thesupercharging efficiency of the compressor 2 and perform efficientcooling inside the electric motor 3. Typically, it is preferable tointroduce the outside air by adjusting the control valve 19 so that thetemperature of the motor coil 11 is in the range of 150 to 200° C.

In the above described case, the opening degree of the control valve 19is controlled based on the detection value of the temperature sensorattached to the motor coil 11, but a control example is not limited tothis. For example, if it is difficult to install the temperature sensorto the motor coil 11, the temperature sensor may be installed in otherlocation and estimate the temperature of the motor coil 11.Alternatively, the temperature sensor may be installed in the inverterunit 4 which is another component that easily generates heat, or theopening degree of opening degree of the control valve 19 may becontrolled based on parameters other than the temperature, such as themotor rotation speed.

The inverter unit 4 is attached to the side of the motor housing 8 wherethe gas supply port 13 is formed, and the element circuit board 22 isaccommodated in the inverter housing 21. The element circuit board 22 isincorporated with elements constituting the inverter circuit and isvertically fixed to the inside of the inverter housing by a support (notshown). By providing a plurality of through holes in the element circuitboard 22 and fixing the element circuit board 22 to the support, theoutside air passes through the inverter unit 4 and then enters the firstcooling passage 17 and the second cooling passage 18 smoothly from thegas supply port 13 provided in the motor housing 8.

Particularly, an air hole 23 is formed in the element circuit board 22at a location corresponding to the gas supply port 13 provided in themotor housing 8. Further, an opening hole 24 is formed in the inverterhousing 21 at a location corresponding to the air hole 23. As a result,it is configured so that the outside air can be introduced more smoothlyto the first cooling passage 17 and the second cooling passage 18 fromthe outside of the inverter unit 4.

Cooling pins 25 are provided on the side wall surface of the inverterhousing 21 and motor housing 8. The cooling pins 25 serve as radiatingfins. By increasing the surface area of the side wall surface forcontact with the outside air, heat dissipation is improved, therebyfurther enhancing the above cooling performance.

The suction force of the negative pressure for drawing in the outsideair weakens if the above-described cross-sectional areas of the firstcooling passage 17 and the second cooling passage 18 are set wide. Thus,the cross-sectional areas of the first cooling passage 17 and the secondcooling passage 18 are arbitrarily set according to the coolingperformance required by the electric motor 3, the value of the negativepressure at the inlet port 5, etc. More specifically, from the viewpointof increasing the suction force for drawing in the outside air, it ispreferable to set the cross-sectional areas of the first cooling passage17 and the second cooling passage 18 as small as possible.

In the case where it is difficult to apply a sufficient negativepressure to the first cooling passage 17 and the second cooling passage18 using a single gas discharge port 14, a plurality of the gasdischarge ports 14 may be provided in the motor housing 8 and each ofthe gas discharge ports 14 may be connected to a separate suctionpassage.

As described above, according to the electric supercharger 1 of thepresent embodiment, by applying a negative pressure from the intakepassage 15 to the cooling passages 17 and 18, it is possible tointroduce the outside air from the gas supply port 13 and cool theperipheral part of the cooling passages 17 and 18 which easily produceheat. In the electric supercharger apparatus 1 according to thisembodiment, the outside air is introduced using the negative pressure ofthe compressor 2 without the configuration that accompanies energyconsumption, such as a pump. Thus, the interior of the motor housing 8with a large calorific value can be effectively cooled with the simplestructure. Particularly, as the outside air is introduced to the coolingpassages 17 and 18, instead of supercharged air of high temperature,excellent cooling effect can be achieved. Especially, the second coolingpassage 18 is reduced in pressure by the negative pressure appliedthereto and hence, air resistance of the rotor shaft is reduced. As aresult, it is possible to achieve reduction of windage loss at the sametime.

Second Embodiment

FIG. 3 is a cross-sectional view of the overall configuration of theelectric supercharging apparatus 1 according to a second embodiment. Inthe following embodiments, components already described in reference tothe first embodiment are denoted by the same reference numerals, andthus detailed description thereof is appropriately omitted.

In the second embodiment, an auxiliary vacuum pump 26 not shown(hereinafter referred to as “negative pressure pump 26”) for the engine(not shown) to which the electric supercharging apparatus 1supercharges, the negative pressure is supplied to the gas exhaust port14 and the outside air is introduced into the first cooling passage 17and the second cooling passage 18 to perform the cooling. The negativepressure pump 26 is connected to the gas discharge port 14 via thesecond intake passage 27, and a second control valve 28 is for adjustingan opening degree is provided in the second intake passage 27. Togetherwith the first control valve 19, the opening degree of the secondcontrol valve 28 is controlled by the controller 20 so as to adjust thenegative pressure value transmitted to the first cooling passage 17 andthe second cooling passage 18.

Herein, a control example of the second embodiment is described indetails. First, it is assumed that the second control valve 28 isbasically set to “closed” and that application of the negative pressureto the first cooling passage 17 and the second cooling passage 18 isperformed using the first control valve 19. In such a case, thetemperature inside the motor housing 8 rises depending on the operatingstate of the electric motor 3 and it is sometimes difficult to obtainthe cooling performance required for cooling solely by the negativepressure from the negative pressure outlet port 16 (That is, it may notbe possible to introduce enough outside air into the first coolingpassage 17 and the second cooling passage 18 solely by the negativepressure from the negative pressure outlet port 16). In such a case, thecontroller 20 controls the second control valve 28 to open so as to makeup shortage of the negative pressure from the negative pressure outletport 16 with the negative pressure from the negative pressure pump 26.

In the present embodiment, by providing a plurality of negative pressuresupply sources (the negative pressure outlet port 16 and the negativepressure pump 26), if enough outside air cannot be introduced by thenegative pressure from one of the negative pressure supply sources, thenegative pressure from the other can be supplied supplementarily so asto enhance the cooling performance. This type of control for the firstcontrol valve 29 and the second control valve 28 may be performed bydetecting a temperature of the motor coil 11, the element circuit board22 in the inverter unit 4, etc. using a temperature sensor such as athermistor and a thermocouple and adjusting the opening degree of eachof the first control valve 29 and the second control valve 28 based onthe detection value.

Third Embodiment

Next, in reference to FIG. 4, explained is the case where the electricsupercharging apparatus 1 according to the present invention is appliedto an electric e-stage supercharging system configured by combining theelectric supercharging apparatus 1 according to the present inventionwith a turbocharger 110 which is driven by the exhaust gas from anengine 100. FIG. 4 is a block diagram of an overall configuration of theelectric 2-stage supercharging system according to a third embodiment.

The electric 2-stage supercharging system according to the presentembodiment comprises a turbocharger 110 on a low pressure side (adownstream side) as a supercharging unit for the engine 100. Theturbocharger 110 has a compressor 112 which operates in conjunction withan exhaust turbine 111 driven by the exhaust gas from the engine 100.Further, the electric supercharging apparatus 1 which is powered by theelectric motor described in the above embodiments is provided on a highpressure side (an upstream side). On the exhaust turbine 11 side of theturbocharger 110, a wastegate valve 113 is provided. On the intake sideof the electric supercharging apparatus 1, a bypass passage 121 equippedwith a bypass valve 120 is provided. Further, the compressed gasdischarged from the electric supercharging apparatus 1 arranged on thehigh pressure side is cooled by an intercooler 130 and then supplied tothe engine 100.

In this electric 2-stage supercharging system, the compressed gas issupercharged in the turbocharger and then further compressed in theelectric supercharging apparatus 1. The compressed gas undergoes twostages of supercharging, and the supercharging pressure can be enhanced.As a result, compared to the case where only the turbocharger 110 isprovided as a supercharging unit, it is possible to obtain highsupercharging pressure and thus, it is possible to realize the systemcapable of performing even when the required output is large, such asduring acceleration.

In this embodiment, the negative pressure outlet port 16 (see FIG. 1 andFIG. 3) to which the first intake passage 15 is connected in theelectric supercharging apparatus 1 is provided on the intake side of theturbocharger 110. As a large negative pressure is generated on theintake side of the turbocharger 110 than on the exhaust side of theturbocharger 110, by providing the negative pressure outlet port 16 onthe intake side of the turbocharger 110 as described above, a largenegative pressure can be applied to the cooling passages 17 and 18formed in the motor housing 8 of the electric supercharging apparatus 1so as to obtain better cooling performance. At the same time, the effectof reducing the pressure in the cooling passages 17 and 18 may beobtained greatly and thus, the air resistance around the rotor shaft 10is reduced, and this contributes to a reduction in windage loss.

In the case shown in FIG. 4, the turbocharger 110 utilizing the exhaustgas on the low pressure side is used. This is, however, not restrictiveand a VG turbocharger, a VFT turbocharger, a 2-stage turbocharger, amechanical supercharger and the like may be used.

Further, as described above, by using the grease-enclosed rollingbearing as the rolling bearing 12 for supporting the rotor shaft 10 ofthe electric motor 3 belonging to the electric supercharging apparatus1, unlike the case of the rolling bearing using the lubricating oil, theengine 100 does not need to be supplied with lubricating oil. Therefore,the electric supercharging apparatus 1 does not need to be installednear the engine 100 in consideration of the supply of the lubricatingoil and can be mounted on a place away from the engine, such as avehicle body, with less vibration and breathability which is suitablefor cooling. More preferably, by arranging the electric superchargingapparatus 1 near the power supply system such as a battery, wiringresistance is less which leads to improved performance. There is anadvantage that the electric supercharging apparatus 1 according to thepresent invention has less restricted installation position within thevehicle body as described above and high flexibility of the layout.

INDUSTRIAL APPLICABILITY

The present invention is applicable to an electric superchargingapparatus and a multi-stage supercharging system using the electricsupercharging apparatus, which is driven by an electric motor forsupercharging an internal combustion engine such as an engine.

REFERENCE SIGNS LIST

-   1 Electric supercharging apparatus-   2 Compressor-   3 Electric motor-   4 Inverter unit-   5 Inlet port-   6 Compressor wheel-   7 Compressor cover-   8 Motor housing-   9 Stator-   10 Rotor shaft (Rotator)-   11 Motor coil-   12 Rolling bearing-   13 Gas supply port-   14 Gas discharge port-   15 Intake passage (First intake passage)-   16 Negative pressure outlet port-   17 First cooling passage-   18 Second cooling passage-   19 Control valve (First control valve)-   20 Controller-   21 Inverter housing-   22 Element circuit board-   23 Air hole-   24 Opening hole-   25 Cooling pin-   26 Negative pressure pump-   27 Second intake passage-   28 Second control valve-   100 Engine-   110 Turbocharger-   111 Exhaust turbine-   112 Compressor-   113 Waste gate valve-   120 Bypass valve-   121 Bypass passage-   130 Intercooler

The invention claimed is:
 1. An electric supercharging apparatus whichis configured to rotate an electric motor that comprises a rotor shaftrotatably supported in a motor housing to which a motor coil and astator are fixed, so as to drive and supercharge a compressor connectedto one end of the rotor shaft, the electric supercharging apparatuscomprising: a gas supply port and a gas discharge port which areprovided in the motor housing; wherein the gas discharge port in themotor housing is connected to an intake passage, and wherein the gassupply port opens to another end side of the motor housing opposite toone end side at which the motor housing is connected to the compressor,a cooling passage which connects the gas supply port and the gasdischarge port in the motor housing and which is formed in the statoralong the motor coil in an outer periphery of the motor coil; whereinoutside air is introduced to the cooling passage from the gas supplyport by a negative pressure of an inlet port of the compressor appliedto the cooling passage via the intake passage; and an inverter unitcomprising an element circuit board housed in an inverter housing, theinverter unit being mounted on a side of the motor housing where the gassupply port is formed.
 2. The electric supercharging apparatus accordingto claim 1, wherein the cooling passage includes a plurality of coolingpassages each of which connects the gas supply port and the gasdischarge port, each of the plurality of cooling passages surrounds themotor coil in a section orthogonal to the rotor shaft.
 3. The electricsupercharging apparatus according to claim 1, wherein the coolingpassage is configured in part to include an outer wall surface of themotor coil.
 4. An electric supercharging apparatus which is configuredto rotate an electric motor that comprises a rotor shaft rotatablysupported in a motor housing to which a motor coil and a stator arefixed, so as to drive and supercharge a compressor connected to one endof the rotor shaft, the electric supercharging apparatus comprising: agas supply port and a gas discharge port which are provided in the motorhousing; wherein the gas discharge port in the motor housing isconnected to an intake passage, and wherein the gas supply port opens toanother end side of the motor housing opposite to one end side at whichthe motor housing is connected to the compressor; a first coolingpassage which connects the gas supply port and the gas discharge port inthe motor housing and which is formed in the stator along the motor coilin an outer periphery of the motor coil; and a second cooling passagewhich connects the gas supply port to the gas discharge port in themotor housing and which is formed along the rotor shaft between therotor shaft and the motor coil, wherein the second cooling passage joinsthe first cooling passage in the motor housing and outside air isintroduced to the first cooling passage and the second cooling passagefrom the gas supply port by a negative pressure of an inlet port of thecompressor applied to the first cooling passage via the intake passage.5. The electric supercharging apparatus according to claim 4, whereinthe first cooling passage includes a plurality of cooling passages eachof which connects the gas supply port and the gas discharge port, eachof the plurality of cooling passages surrounds the motor coil in asection orthogonal to the rotor shaft.
 6. The electric superchargingapparatus according to claim 4, wherein the first cooling passage isconfigured in part to include an outer wall surface of the motor coil.